The present invention relates to new orthoester-based block polymers having a good antifoaming effect in liquid aqueous systems. The compounds are easily biologically degradable and, compared with traditional block polymers, have a comparatively high cloud point, which makes them readily compatible with other compounds and facilitates the formulation of homogeneous compositions.
Block polymers containing hydrophobic blocks based on alkylene oxides, such as propylene oxide and/or butylene oxide, and hydrophilic blocks based on ethylene oxide, are a well-known group of compounds having a good antifoaming effect in liquid aqueous systems. However, they are difficult to degrade biologically and have relatively low cloud points. Other types of compounds with antifoaming effect are silicone compounds, which in many applications cannot be used owing to the absorption of the silicone compounds to solid materials. Other examples are nonionic surface-active ethylene oxide adducts, where the ethyleneoxy chain has been terminally blocked with one or more alkyleneoxy alkyl groups having 3-4 carbon atoms or an alkyl group having 1-4 carbon atoms. These compounds are in themselves low-foaming and thus not very efficient as antifoaming agents. Besides, they are comparatively difficult to degrade biologically.
EP 564 402 discloses the preparation of surface-active low-foaming orthoesters by using as reactant an addition product of ethylene oxide to a hydroxyl-containing aliphatic compound having 8-26 carbon atoms. The resulting products have higher foaming than traditional block polymers between ethylene oxide and propylene oxide and are not suitable for use as antifoaming agent. Moreover, in degradation ethylene oxide adducts are formed, which are foaming and have high surface activity, which are inconvenient properties from the viewpoint of application as well as environment. Alkylene-glycol-containing orthoesters are also disclosed in U.S. Pat. No. 2,867,667 and U.S. Pat. No. 3,903,006. The latter patent specification states that owing to, among other things, a suitable viscosity at xe2x88x9240xc2x0 C., it can be used in hydraulic fluids.
The object of the present invention is to find compounds which have a good antifoaming effect at least on the same level as known block polymers and which are easily biologically degradable and, in degradation, form intermediate products having low foaming, toxicity and surface activity. Moreover, they should have good wettability and high cloud points.
It has now been found that orthoester-based polymers have a good antifoaming effect in liquid aqueous systems, while they are easily biologically degradable compared with conventional block polymers. The intermediate products formed in degradation have low foaming, toxicity and surface activity. Besides, the hydrophobic-hydrophilic balance of the compounds can easily be changed such that the wettability and cloud point in water are adapted to the properties desired for different applications. The new polymers are of the general formula 
wherein R1 is hydrogen or a hydrocarbon group having 1-4 carbon atoms; R2 is a group (A)nY, where each A is an ethyleneoxy group or a higher alkyleneoxy group having 3-4 carbon atoms, n is a number 0-100, and each Y is hydrogen or an alkyl group having 1-4 carbon atoms, provided that when Y is hydrogen, n is a number from 1 to 100, R3 and R4 are groups of the formula (A)nY, where A, n and Y have the above meaning, or a di- or polycondensate of the polymers via free hydroxyl groups in R2, R3 or R4, the total sum of all n being 8-2, 500, preferably 8-200, and that at least one of the groups R2, R3 and R4 contains at least one block of at least 4, usually 4-50, preferably 6-20 alkyleneoxy groups having 3 and/or 4 carbon atoms. Preferred polymers are those where the total number of ethyleneoxy groups in the polymers is 0-80%, preferably 5-60%, based on the total number of alkyleneoxy groups and higher alkyleneoxy groups and a molecular weight of 600-100,000, preferably 800-10,000.
By varying the number and types of alkyleneoxy groups in the groups R2, R3 and R4 and their positioning in the groups, and by terminally blocking the groups with alkyl groups, the properties, such as solubility, cloud point, floatability, wettability, melting point and antifoaming effect, of the orthoester-based block polymers can be varied and combined in various ways according to their different fields of application. In contrast to traditional block polymers, which usually have an antifoaming effect which is strongly temperature-dependent, the inventive block polymers, which usually are present in the form of a product mixture, have low sensitivity to variations in temperature and can therefore be used in wide temperature ranges. Examples of fields where the block polymers can be used as antifoaming agent are in milk substitute compositions, in chemical processes, such as emulsion polymerisation, in metal working fluids and other industrial functional fluids, in dishwasher formulations and in industrial cleaning, in cosmetics, lubricants and liquid plant protection compositions etc.
Examples of suitable polymers according to the invention are those of the general formula 
wherein R1 has the above meaning, each A1 is an alkyleneoxy group having 3-4 carbon atoms, m is from 4 to 40, each Y1 is hydrogen or an alkyl group having 1-4 carbon atoms, each A2 is an alkyleneoxy group having 2-4 carbon atoms, Y2 is hydrogen or a hydrocarbon group having 1-4 carbon atoms, n is a number from 2 to 40, Y3 is an alkyl group having 1-4 carbon atoms, x is 1, 2 or 3, preferably 1 or 2, y is 0, 1, 2 or 3, preferably 0 or 1, and z is 0, 1 or 2, preferably 0 or 1, the sum of x, y and z being 3. Preferably Y1 and Y2 are an alkyl group having 1-4 carbon atoms. When preparing the compounds according to the invention, a mixture of compounds according to the invention is usually obtained owing to the process of preparation. A common average value of x is 1.0-2.1, y is 0.1-1.8 and z is 0.2-1.8. In formula II, Y1, Y2 and Y3 are preferably a methylene or ethylene group. The groups A1 are preferably propyleneoxy groups, while the groups A2, usually to at least 10%, preferably to at least 50%, consist of ethyleneoxy groups. If A2 consists of both ethyleneoxy and higher alkyleneoxy groups, these can be added in blocks or at random, or a combination thereof.
The compounds according to the invention can be prepared by reacting, in one or more steps, an orthoester of the general formula 
wherein R1 has the above meaning and Y4 designates a hydrocarbon group having 1 or 4 carbon atoms, with reactants of the formulae HOR2, HOR3 and HOR4, wherein R2, R3 and R4 have the above meaning, suitably in the presence of an acid catalyst, such as methanesulphonic acid. As the reaction proceeds, the released hydroxyl-containing compound Y4OH is removed, where Y4 has the above meaning, at an increasing temperature, which in the final phase of the reaction suitably is 140-220xc2x0 C. The final phase of the reaction is usually also carried out under vacuum. Conveniently, the reaction is carried out in several steps. For example, the reactants containing secondary hydroxyl groups can be reacted before reactants containing primary hydroxyl groups. If dimerisation or a higher degree of merisation is desired, diols having in the first place primary hydroxyl groups, but also diols having secondary hydroxyl groups are suitably selected, and triols or hydroxyl compounds having a large number of hydroxyl groups, which optionally are secondary, may be used.